Heterosexual Life Partners/Video Games/Visual Novel

In Katawa Shoujo we have Hanako and Lilly. The reason for this is that Hanako is an extreme social recluse, to the extent that she depends on Lilly just to help her cope at school, while Lilly has taken a role very similar to that of a mother in taking care of her. This trope is so in effect that their routes in Act 1 don't split until the very end, and each of their routes beyond that still feature the other heavily. In Lilly's route, Hisao even comments that they're sort of like an odd family altogether, with him and Lilly as the parents and Hanako as the child.